Switching devices with one or several current paths, which comprise fixed or movable contacts, are generally used for switching off currents in consumer networks. The movable contacts can be moved jointly between a closed position, where the movable and fixed contacts touch each other, and an open position, where there is a separating path established between the movable and fixed contacts, which are assigned to each other. When the movable contacts under load, i.e. under the current flow, are moved in the open position, arcs are formed along the separating paths. The burning time of the arc determines the switching time because the current flow is maintained between the contacts. Furthermore, the arcs produce a significant amount of heat, which cause the thermal destruction of the contacts and components of the switching chamber located near the contacts and thus result in reducing the useful life of the switching device. The arc must therefore be extinguished as quickly as possible by the arc extinguishing devices. The extinguishing devices separate the arcs, for example, into individual partial arcs. As soon as the arc voltages exceed the driving voltages, the arcs are securely extinguished.
The magnetic fields generated by the currents themselves are often used for extinguishing especially high currents to drive the forming switching arcs independently quickly away from the contacts toward the extinguishing devices, where they are finally extinguished.
In case of switching devices for direct current, the arc is not interrupted independently as in case of the zero passage of the alternating current. Therefore, in cases of direct current applications, blow magnets are used that generate a magnetic field with a given strength and orientation, which generates a deflecting force (Lorentz force) on the arcs that deflects the arcs to the arc extinguishing devices. In the extinguishing devices, the arcs are stretched, cooled, separated into partial arcs and extinguished in this manner.
Such a switching device as specified in the outset is known from EP 2 061 053 A2. For creating a switching device for direct current applications, it is recommended that the housing of a switching device for alternating current applications be used, where at least one magnet is provided in addition, which creates a magnetic field with field lines predominantly transverse to the isolation gaps of current paths of the alternating current switching device. There are three receiving regions in the housing for each single current path, where each current path is assigned a movable switching contact element as well as two fixed switching contact elements opposite to each other. The three movable switching contact elements can be moved together, between a closed position which corresponds to the switched-on state of the switching device, and an open position which corresponds to a switched-off state of the switching device. The individual current paths are each assigned two arc extinguishing devices in the form of extinguishing plates, arranged individually over one another and electrically insulated from each other. In addition, each current path has two separation sections which, when the movable switching contact elements are open, form between the ends of the movable switching elements and the first and second fixed switching elements which are allotted to the ends of the movable switching contact elements. On opening of the switching contact elements, an arc which can be extinguished with the help of arc extinguishing devices is formed along each separation section. In direct current applications, the arc cannot be extinguished at the zero current passage, as in alternating current applications, and therefore a magnetic field must be used in most direct current applications to drive the arc into an arc extinguishing device. This magnetic field is built up by permanent magnets, where a magnetic field is generated with field lines in a direction which runs transverse to the separation sections and creates a Lorentz force on the arcs that form along these separation sections which drives the arc in the direction of an arc extinguishing device. In this context, an arc between a first contact pair is driven in the direction of a first arc extinguishing device and the arc between a second contact pair is driven in the direction of the second arc extinguishing device. Since the movement of the arcs is dependent on the direction of the current, the switching device is only suitable for one current direction, i.e. polarity. If the switching device is operated in the opposite current direction, the arcs will not be driven into the arc extinguishing devices but in the opposite direction to a switching bridge. Even if the magnetic polarity of one of the arc extinguishing devices is reversed, one of the arcs would run towards a switching bridge, which would result in reduced lifetime, since the switching bridge or other part would be damaged or even destroyed in the long run.
The EP 0 789 372 B1 also shows a switching device of the type mentioned at the outset. A fixed contact is provided with a fixed arc runner which is circular arc-shaped. A movable arc runner is provided on a movable contact, where an arc can form between the two arc runners, which can be moved in different directions by the arc driver assembly in accordance with the direction of the current. In accordance with the direction of current, this is diverted around a center point, either in the first direction of rotation or in a second direction of rotation opposite to the first, where the center point corresponds to the center point of the fixed arc runner. An arc with the first direction of current is diverted into a first arc runner channel and an arc with a direction of current opposite to the first direction of current is diverted into the second arc runner channel. Both arc runner channels run around the center point and are arranged next to each other separated by an insulating wall. The arc runner channels are part of an extinguishing device for extinguishing the arc. Furthermore, the extinguishing devices comprise extinguishing plates which are radially oriented to the stationary arc channels. The extinguishing plates are arranged in such a way that they cover both the arc channels and, therefore, are part of both extinguishing devices.
In many known switching devices, the arc formed during switching is driven in a blowout field generated by a permanent magnet into an extinguishing chamber, for example, a deion extinguishing chamber, to be extinguished there. The guide rails of the arc guiding devices run from the contacts to the outside in diverging directions.
Depending on the polarity of the current, immediately after its creation, the switching arc is driven by the Lorentz force away from the switching contacts along one of the two guide rail arrangements, which run diametrically apart, in the direction of the extinguishing chamber, where the arc is normally quickly extinguished when reaching the driving voltage.
In switching arcs with high energy content, especially with a high inductive share in the current circuit, it can happen that the arc entering the extinguishing chamber only loses part of its energy in the chamber and is not completely extinguished. In that case, re-ignitions can occur after passing through the extinguishing chamber by the arc moving from the outside end of the extinguishing chamber to the end of the guide rail and in certain cases running again in the direction of the contacts. Depending on the geometry of the switching chamber, the arc can also burn steadily at certain locations, for example at the terminations of the guide rails, which causes an extension of the burning time of the arc and therefore a higher thermal load on the switching chamber, which can cause a reduction of the electrical useful life of the switching device.